Yeah, the "well you'd have to ban pencils" argument is pretty flawed.
First, you can do what's a called a "cost-benefit analysis". Very few people get stabbed with a pencil vs the number shot with guns. So the costs of banning pencils outweigh the benefits. For guns, the math is completely different. It's a complete red herring to say that gun control isn't worthwhile because there's a theoretical chance of dying by falling on a pencil: what matters is the cost-benefit analysis of the gun control legislation.
e.g. the flaw in the pencil argument is that it's really arguing that if you can't get absolute safety, e.g. 100% safety then it makes no sense to value relative safety, e.g. it's not worth striving for 99% safety, because 99% is less than the hypothetical safety of 100%. But of course, the argument that being "safer" is worthless unless it's "the safest" is flawed.
By induction, if 99% safety isn't worthwhile because it's less than 100%, then 98% isn't worthwhile because it's less than 99%, and so on, and ultimately, you can use the same argument to argue that making things even 1% safe isn't worthwhile. e.g. why not let companies put lead back in the paint? After all, other substances cause brain damage too, and you're going to die eventually anyway. So we might as well enjoy brightly-colored paint while we're alive, and not worry about toxic brain damage at all. That's the same argument as the "but pencils can kill you" argument.
Also, of course by the deadly-pencils logic you'd need to let people open-carry hand grenades and bazookas. After all, why ban those when people will just weaponize stationary if they can't use them? Or how about letting people carry buckets of acid around to throw into people's faces? That should be perfectly acceptable, too, because they could just take your eye out with a pencil, so why bother trying to prevent acid attacks at all? Of course the point here is that if anyone objects to people carrying around weaponized acid and explosives because there should be limits because those things are just too deadly or horrific, then that contradicts the whole "but pencils can kill" argument.